The autotaxin (ATX)->lysophosphatidic acid (LPA)->LPA-receptor (LPAR) signaling axis stimulates the proliferation, motility, invasion, and metastasis of tumor cells; its components are upregulated in several carcinomas. During the prior funding period, we made major discoveries about ATX -> LPA -> LPAR axis as important oncogenic mechanisms, which now provide the fundamental principles from which to propose developing drug-like compounds that prevent cancer invasion and metastasis by disrupting this signaling axis. ATX, a lysophospholipase D that generates LPA, is among the 40 most upregulated genes in metastatic cancers. Overexpression of ATX or LPAR leads to malignant transformation, metastasis, and resistance to cell death. Our laboratory evidence to date shows that: 1) Selective inhibitors of ATX inhibit metastasis. 2) LPA1- receptor knockout (KO) mice are completely resistant to metastasis of B16 syngeneic melanoma. 3) An LPA1/3 antagonist markedly reduces melanoma metastasis. 4) LPA bromophosphonate, a dual-action inhibitor of ATX and also antagonist of LPA1/2/3/4 receptors, not only inhibits metastasis but also inhibits tumor growth in vivo. Based on these findings, we propose to test three translational hypotheses: 1) Long-lasting inhibition of ATX-mediated LPA production by cancer cells will inhibit tumor metastasis. 2) Inhibition of LPA1 in the host will block metastasis. 3) Multi-targeting of ATX and LPA1 will reduce tumor growth and provide superior chemoprevention against metastasis over monotherapy. First, we will improve small-molecule ATX inhibitors to achieve long-lasting reduction of LPA production in the tumor microenvironment. To this end, we will increase the structural diversity of available ATX inhibitors and improve the LPA1 receptor specificity of our dual-action ATX inhibitor/LPAR antagonist leads by using high throughput screening, in silico drug design utilizing the new ATX crystal structure, and medicinal chemistry. We will mechanistically characterize the most potent leads in enzymatic and cancer invasion assays in vitro and determine their toxicokinetic profiles in vivo. We will compare the in vivo efficacy of new ATX-specific inhibitors alone, in combination with the LPA1- specific antagonist AM095, and the dual-action ATX/LPA1 inhibitors in different murine metastasis models. We envision that the drug candidates we will identify will ultimately be used as part of the multimodal treatment of cancers for the prevention of metastasis prior to/after removal of the primary tumor as is often the case for melanomas.